Croatia's Football Federation (HNS) faces fresh disciplinary proceedings over incidents during Monday night's 1-0 defeat by Spain in Gdansk.
The HNS was fined £65,000 by Uefa on Monday after fans racially abused Italy striker Mario Balotelli.
Uefa has opened a new improper conduct case over racist banners displayed by fans during the Spain game.
The Federation also faces punishment over the conduct of its team after six players were booked on Monday.
A Uefa statement read: "Uefa has today opened disciplinary proceedings against the Croatian Football Federation (HNS) for the setting-off and throwing of fireworks, and the improper conduct of supporters (display of racist banners and symbols) at the EURO 2012 Group C match against Spain in Gdansk on Monday.
"The disciplinary case also involves the improper conduct of the team (six Croatian players received a yellow card during the match)."
Uefa will deal with the new case on Sunday.
It is the third time at Euro 2012 that Croatia's Football Federation has been in trouble over fan behaviour.
Last week, the HNS was fined £20,000 after supporters let off flares during Croatia's 3-1 win over Republic of Ireland.
Then on Monday, Uefa imposed a further fine over the abuse of Balotelli during Croatia's 1-1 draw against Italy.
A photographer reportedly saw a steward retrieving a banana and heard monkey chants directed at the Italy and Manchester City striker.
Fare (Football Against Racism in Europe) announced that its observers heard between 300 and 500 Croatia fans chanting monkey noises, which prompted Uefa to investigate.
That punishment also related to the setting off and throwing of fireworks.
But the scale of the fine was £15,000 less than the £80,000 Uefa gave to Denmark striker Nicklas Bendtner for revealing sponsored pants.
That sparked criticism from Manchester United defender Rio Ferdinand and Manchester City captain Vincent Kompany.
The HNS, which last week labelled its misbehaving fans "deviant", has been previously fined twice for racism by Uefa and Fifa since 2008.
Croatia's defeat by Spain saw them knocked out of Euro 2012, finishing third in Group C behind the reigning champions and Italy.